Pumps of both the fixed and free type often include a control valve means axially positioned above an engine and a production pump means, and it is not unusual for the engine chambers to be positioned at each extremity of the production pump means, as evidenced by my previous U.S. Pat. No. 3,650,640. However, in this particular fixed-typed pump, provisions must be made within the side wall of the pump housing for various fluid flow paths, as for example, from the valve means to the engine means, and consequently, the diameter of the pistons thereof are reduced a corresponding amount.
Some oil wells are extremely deep and small in diameter and require a slim pump for accommodation within the slim borehole. Some of these walls are high volume producers and require a high volume pump. Accordingly, the present invention provides an improvement over U.S. Pat. No. 3,650,640 by the provision of both a fixed and a free-type downhole pump assembly which eliminates the heretofore necessary internal flow passageways formed within the side wall of the production pump and engine housing. This improvement is brought about by a novel combination of flow passageways formed externally of the pump housing and other passageways formed within the reciprocating, centrally located, control rod of the pump assembly.
The present invention further provides a novel hydraulic pump assembly which operates in a manner to eliminate rod breakage by arranging the component parts thereof to always place the connecting rod in compression during both the up and down stroke.
The above combination of elements provide a multistage pump which can be assembled to employ any number of engine and production pistons to thereby increase the production rate, while at the same time lowering the pressure required of the power fluid.